Conventionally, as one of the molding methods using an injection molding machine, there has been widely performed foam molding in which resin undergoes foaming to be formed into a molding. Various characteristics can be added to the foam molding prepared by this foam molding, such as light weight, thermal insulation property, and acoustic absorption.
As is known, in foam molding, the die cavity is filled with molten resin containing foaming agent, and after the surface layer of the molten resin has been solidified into a skin layer, a core back operation is performed with respect to the die in order to foam the resin (See, for example, Patent Document 1).
Further, according to the disclosure of Patent Document 1, in the core back operation in foam molding using a toggle type die clamping device, a movable platen is controlled with ten times the accuracy with which the position of a cross head is controlled.